Method and device for operating an exhaust-gas after-treatment system

ABSTRACT

The invention relates to a method for operating a motor vehicle exhaust-gas aftertreatment system ( 1 ), in which oxygen is fed to and removed from the oxygen tank ( 8 ) of an exhaust-gas aftertreatment component ( 7 ). According to the invention, the oxygen quantity in the oxygen tank ( 8 ) is determined and a rich-lean cycle is influenced in accordance with the determined oxygen quantity. The invention also relates to a motor vehicle exhaust-gas aftertreatment system ( 1 ), which permits a temperature regulation of the oxygen tank ( 8 ) and/or an uninterrupted desulphation during the transition between a rich operation and a lean operation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the U.S. national phase of international patentapplication PCT/EP2007/004676 filed May 25, 2007, which claims priorityto German patent application DE 10 2006 025 050.8 filed May 27, 2006.

FIELD OF THE INVENTION

The present invention relates to a method for operating a motor vehicleexhaust-gas after-treatment system and also to an exhaust-gasafter-treatment system with a connected internal combustion engine.

BACKGROUND OF THE INVENTION

From U.S. Pat. No. 6,843,052, it is known that a rich-lean cycle can beused so that the oxygen accumulator of an exhaust-gas after-treatmentcomponent is used for the oxidation of H_(s)S. The accumulator is filledduring a lean phase and at least partially emptied during a rich phase.For regulating O₂ content, a lambda probe placed downstream of theexhaust-gas after-treatment component is used. Here, if asubstoichiometric air ratio is detected, a lean transition is triggered.For a hyperstoichiometric air ratio, a rich transition is triggered. InEP 0 893 154 B1, an oxygen accumulator connected downstream of anNOx-accumulating catalytic converter (NAC) is used for supplying oxygenfor the H₂S oxidation.

From DE 197 47 222 C1, an internal combustion engine system with NAC andsecondary air injection with a method for desulfurization of the NAC isknown. In this system, the desulfurization control system is regulatedby the output signal of a lambda probe placed downstream.

From DE 198 27 195 A1, it is known that for a lean-rich transition,initially SO₂ is produced for a short time and formation of H₂S followswith a time delay. Therefore, H₂S emission can be suppressed by an earlyrich-lean transition.

In DE 101 26 455 A1, a method for the desulfurization of an NAC isdescribed that follows the regeneration of a particulate filter, wherebythe heating to a desulfurization temperature is eliminated or shortened.

From DE 199 22 962 C2, it is known that the air ratio in the exhaust gascan be set by supplying secondary air during NAC desulfurization.

The regulation or control system concepts emerging from the abovedocuments relate to a lambda probe signal downstream of anoxygen-storing component in the exhaust-gas train. Especially at hightemperatures, the lambda probe here shows a value that is not equal toone only when an oxygen accumulator is completely filled (λ>1) or iscompletely empty (λ<1). Therefore, e.g., for desulfurization, richbreakthroughs with accompanying H₂S emission can appear.

SUMMARY OF THE INVENTION

The task of the present invention is to create an improvement in theoperating behavior of an exhaust-gas after-treatment system that takesinto account, in particular, the actual conditions in an exhaust-gasafter-treatment system and allows a rapid and also reliable reaction.

This task is achieved with a method with the features of claim 1 andalso with an exhaust-gas after-treatment system with the features ofClaim 19. Other advantageous configurations are specified in eachsubordinate claim.

According to the invention, a method for operating a motor-vehicleexhaust-gas after-treatment system is proposed in which oxygen is fed toand removed from an oxygen accumulator of an exhaust-gas after-treatmentsystem, wherein at least one variable parameter influenced by the oxygenaccumulator and its oxygen content is determined and is used foroperation of the motor-vehicle exhaust-gas after-treatment system.

Advantageously, the oxygen quantity in the oxygen accumulator isdetermined and, according to one improvement, a rich-lean cycle isinfluenced as a function of the determined oxygen quantity. For example,an oxygen quantity in the oxygen accumulator can be included as aparameter for setting a rich-lean cycle. An example configurationprovides that the oxygen quantity is used as a regulating or controlparameter for a rich-lean cycle. Another example configuration providesthat an oxygen quantity in the oxygen accumulator is regulated by meansof at least one rich-lean cycle, advantageously by means of differentrich-lean cycles. One possible realization has a motor control systemthat controls or regulates the rich-lean cycles, wherein the oxygencontent in the oxygen accumulator is controlled or regulated. For thispurpose, the motor control system can use, for example, a plurality ofcharacteristic engine maps or an oxygen calculation that is performedcontinuously or discontinuously.

In particular, a fill level of the oxygen accumulator is taken intoaccount. Thus, for control or regulation systems with respect toindividual components or all of the components of the exhaust-gasafter-treatment system, not only is a lambda probe signal taken intoaccount, but the current state of the oxygen accumulator is detected andtaken into account insofar as this is in the position, for example, todischarge oxygen for operation in a rich section of the rich-lean cycleor, conversely, to be able to store oxygen in a lean range of therich-lean cycle.

In addition, an additional oxygen supply into the motor-vehicleexhaust-gas after-treatment system can be provided as a function of thedetermined oxygen quantity of the oxygen accumulator. Such an oxygensupply can be performed, for example, by means of an air supply, alsolike an oxygen supply into the exhaust-gas after-treatment system. Thereis also the possibility, for example, to change the air supply in theexhaust-gas after-treatment system additionally or also independentlythrough corresponding valve overlap in a connected internal-combustionengine.

Preferably, the oxygen quantity is calculated by means of an oxygenbalance across the oxygen accumulator. This can be realized, forexample, by means of a first probe and a second probe. The first probeis preferably arranged in the flow direction before the oxygenaccumulator, advantageously at least directly before the oxygenaccumulator. The second probe is preferably arranged in the immediatevicinity downstream of the oxygen accumulator. In addition, there is thepossibility that at least one of the two probes is arranged directly onan opening of the oxygen accumulator. There is also the possibility thatat least one of the probes is arranged in the oxygen accumulator. Forexample, the entire accumulation behavior of the entire oxygenaccumulator can be determined from the partial behavior of the oxygenaccumulator.

Preferably, a first probe for a continuous measurement of the oxygencontent before the oxygen accumulator is used. Here, instead of theoxygen content, the air content before the oxygen accumulator can alsobe determined, and the oxygen content can be determined from this. Thesecond probe preferably determines the oxygen content after the oxygenaccumulator, at least at time intervals. It is preferred that acontinuous measurement of the oxygen content or the air ratio isperformed. For example, it is provided that, of the two probes, at leastthe probe in front in the flow direction is a broadband lambda probe. Incontrast, the other of the two probes can be a transition probe.However, two broadband lambda probes can also be used. Advantageously,at least one of the probes is in a position to also record thetemperature.

According to one improvement, the exhaust-gas after-treatment system isequipped with a separate control device. The control device stores,advantageously, not only a control or regulation system with respect tothe oxygen accumulator. Advantageously, other components of theexhaust-gas after-treatment components are also included in the controldevice. In addition to the oxygen accumulator, this can be additionalcatalysts, particulate filters, injection devices in the exhaust-gasafter-treatment system, for example, ammonia-containing means or thelike. A configuration provides that such functionality is implemented ina motor control device. Another configuration provides that the controldevice is arranged separately from the motor control system.

According to one configuration, the method is used to achieve a targetedinfluence on the rich-lean cycle with the oxygen quantity stored in theoxygen accumulator. For example, it is possible through targeted fillingand emptying of the oxygen accumulator to be able to change a quantityof heat released per unit of time. Thus there is the possibility to beable to influence, for example, the temperature of the oxygenaccumulator or a component that has the oxygen accumulator.

For example, it is provided that regeneration of an exhaust-gaspurification component of the motor vehicle has to be performed within acertain temperature range. This is the case, for example, for aregeneration of a diesel particulate filter, as well as for adesulfurization of a nitrogen oxide-accumulating catalytic converter.For example, in a particulate filter, if an internal combustion engineis operated in a lean mode, then soot collects. For burning off soot,advantageously a temperature greater than 500° C. is set. If, forexample, an uncoated particulate filter is used, a temperature greaterthan 600° C. is used. For a catalytically- coated filter, for example, atemperature greater than 550° C. exhaust gas temperature is set on theparticulate filter. According to one configuration, a rich-lean cycle isused for increasing temperature during regeneration. Here, an oxygenaccumulator is at least partially filled and emptied cyclically.Reactions performed in this way in the oxygen accumulator generate heatthat is used for increasing the temperature. The temperature increasecan be performed, for example, before the actual regeneration, so thatfor triggering the actual regeneration, advantageously only littleenthalpy must still be provided. For example, the oxygen quantitypresent in the oxygen accumulator can be used to generate, at leastpartially, a required temperature and/or temperature increase forregeneration. For this purpose, the oxygen accumulator stores oxygenaccordingly in phases of an oxygen excess supply, wherein this oxygencan be output in phases of regeneration.

Such an operation of the oxygen accumulator in interaction withregeneration is supported, for example, in various ways by means of themotor control system and/or the separate control device. For example,the temperature increase can be achieved in such a way that anexhaust-gas temperature is detected at the internal combustion engine orelse also for operation of a turbine at the outlet of the turbine. Forexample, in an internal combustion engine, this can be realized by areduction of the air ratio, for example, by post injection, through achange of an injection angle and also through throttling of the air fedto the engine or a turbine. To allow an amplification of the temperatureincrease, fuel that has not combusted or that has combusted onlyincompletely can be fed to the oxygen accumulator. For example, for thispurpose, a delayed post injection of fuel can be used in an expansioncycle of the internal combustion engine. Furthermore, there is thepossibility to provide an injection of the fuel into a displacementcycle. In addition there is the possibility of direct fuel supply intothe exhaust-gas flow, for example, by means of an additional injection.There is also the possibility of reforming fuel and supplying it assynthesis gas. For example, there is also the possibility that, in amotor vehicle that has a bivalent drive, for example, a liquid gasaccumulator, a natural gas accumulator, or the like is used in addition,in order to allow a corresponding fluid inflow into the exhaust-gasafter-treatment system.

The oxygen to be stored in the oxygen accumulator is fed, for example,from residual oxygen from the engine combustion. However, there is alsothe possibility of providing an external air supply into the exhaustgas. For this purpose, for example, a secondary air fan can be used.There is also the possibility of being able to use a charging device ofan internal combustion engine for this purpose. In addition there is thepossibility of using oxygen stored at other locations of the exhaust-gasafter-treatment system for enriching the oxygen output from this systemin the oxygen accumulator.

A combustible gas component can be converted in the exhaust-gasafter-treatment system through sufficient oxygen made available, forexample, by means of oxygen fed exclusively from the oxygen accumulatoror additionally from the oxygen accumulator, in particular, as asupplement from the oxygen accumulator. For the operation of the motorvehicle exhaust-gas after-treatment system, it is geared in a targetedway to the use of the present oxygen accumulator in a controlled way.For example, there is the possibility of performing a temperaturecontrol or regulation of the particulate filter, in particular, when theparticulate filter itself has the ability to act as an oxygenaccumulator.

According to another configuration, the determined oxygen quantity ofthe oxygen accumulator is included as a parameter in a desulfurizationprocess of an oxide accumulator advantageously for influencing arich-lean cycle. The oxide accumulator can be, for example, a nitrogenoxide-accumulating catalytic converter and/or a sulfur oxideaccumulator. In desulfurization, an oxygen supply from the oxygenaccumulator is used to oxidize, for example, H₂S created duringsubstoichiometric operation into SO₂. By determining the current oxygencontent in the oxygen accumulator, it is advantageously implemented inthe corresponding operating strategy that complete emptying of theoxygen accumulator is avoided especially during rich operation. Thus, arisk of H₂S output is prevented. In particular, if it is provided as anoperating strategy that the oxygen accumulator may never be completelyemptied, then instead of a lambda probe after the oxygen accumulator, inparticular, a transition probe can also be provided.

Advantageously, not just a determination of a beginning of adesulfurization process and/or a regeneration process can be determinedby means of the considered oxygen quantity. There is also thepossibility that the determined oxygen quantity is incorporated as aparameter for determining a time period of the desulfurization and/orthe regeneration.

Advantageously, not just a determination of a beginning of adesulfurization process and/or a regeneration process can be determinedby means of the considered oxygen quantity. There is also thepossibility that the determined oxygen quantity is incorporated as aparameter for determining a time period of the desulfurization and/orregeneration. [sic; repeated paragraph (except for one “the”)]

The oxygen quantity required for the method in the oxygen accumulator isdetermined, according to one configuration, through integration of theoxygen mass flow exchanged with the accumulator. The oxygen mass flow ishere calculated with reference to a difference in the probes, inparticular, the lambda probes, and also the exhaust-gas mass flow. Forthis purpose, the following formula is used:

{dot over (m)}₀₂={dot over (m)}_(A)·L·(λ_(beforeCat)−λ_(afterCat))

m₀₂=∫ {dot over (m)}₀₂dt where

m₀₂—stored oxygen massm₀₂—exchanged oxygen mass flowm₀₂—exhaust-gas mass flowL—stoichiometric factorλ—air ratio

The result of such a calculation or another may be incorrect, forexample, due to inaccurate lambda signals or an inaccurate exhaust-gasmass flow, so that the calculated oxygen content does not correspond tothe actual oxygen content. Also, through integration, an error cancontinue to grow over time. It is then possible that undesired rich orlean breakthroughs are realized. If such a breakthrough should occur,with reference to this breakthrough the actual state of the accumulatorcan be identified and the calculation can be reset to a certain value.In addition, a targeted breakthrough situation can be created, in orderto also achieve a calibration of the measurement. There is also thepossibility for initiating a calibration from the operating behavior ofthe oxygen accumulator. For example, a maximum storage state can also betested through corresponding air or oxygen supply and advantageously acalibration for the storage capacity and the storage state of the oxygenaccumulator can be determined.

One improvement provides that, in the scope of a control or regulationsystem, the oxygen accumulator, advantageously also its oxygen storagecapacity and, in particular, the current, determined stored oxygenquantity are used to set at least one threshold value. When thisthreshold is exceeded, a cycle change is triggered between lean and richoperation. The threshold value can be fixed. However, there is also thepossibility that the threshold value can be adapted, for example, due toaging of the oxygen accumulator. For example, for a calibration of theoxygen storage capacity or the calculation of the oxygen storagecapacity, the threshold value can be increased or decreased. Forexample, the threshold value is stored in the control device of theexhaust-gas after-treatment system. However, it can also be provided,for example, in the motor control system. Preferably it is provided thata lower and an upper threshold are set with respect to the oxygenquantity and a cycle change between lean and rich operation is triggeredwhen the threshold is exceeded. A trigger time point for the cyclechange can here be provided when the threshold is reached but also onlyafter the threshold is exceeded. Preferably, a hysteresis response canbe triggered for a cycle change. This means that after a threshold isreached, the oxygen accumulator either continues to store oxygen in aslowed manner before discharging the oxygen or, in the inverse case, adischarge of the oxygen is performed in a slowed manner before oxygen isstored again in the oxygen accumulator. Advantageously it is providedthat the threshold with respect to the oxygen quantity in the oxygenaccumulator can be exceeded once the threshold is reached and then afterthe cycle change has been completed and the operating behavior withrespect to the oxygen discharge or absorption of the oxygen accumulatorhas been reversed.

In addition, it can be provided that an internal combustion engine isoperated in a rich-lean cycle, wherein a temperature of the oxygenaccumulator is determined and an operating parameter influencing thestored oxygen quantity is changed as a function of the determinedtemperature. In particular, there is also the possibility thattemperature control of the exhaust-gas after-treatment component havingthe oxygen accumulator changes an oxygen quantity discharged per unittime from the oxygen accumulator for adjusting the temperature of theexhaust-gas after-treatment component. In the case of temperatureregulation through the use of the oxygen accumulator, for example, a PIregulator can be used.

In addition, as well as also separately, an operation of themotor-vehicle exhaust-gas after-treatment system can be provided inwhich a rich-lean cycle is performed at least partially duringdesulfurization of an oxide, in particular, a nitrogenoxide-accumulating catalytic converter, and an air ratio is stored afterthe oxide, in particular, the nitrogen oxide-accumulating catalyticconverter, wherein the oxygen quantity is determined and used to preventsubstoichiometry and/or hyperstoichiometry of the air ratio after theoxide, in particular, the nitrogen oxide-accumulating catalyticconverter. Here, reference is made, in particular, to one or morethresholds that can be set with respect to the storage quantity ofoxygen in the oxygen accumulator. For example, there is the possibilitythat not just one threshold value, but several threshold values areprovided. Here there is the possibility to be able to operate the oxygenaccumulator with different temperatures or oxygen discharge or oxygenabsorption.

The operation of the oxygen accumulator is integrated into theexhaust-gas after-treatment concept of the motor vehicle. Therefore, theoxygen accumulator can be arranged as an individual component in theexhaust-gas after-treatment system. It is preferred, however, that theoxygen accumulator is a part of a component of the exhaust-gasafter-treatment system. This can be a catalytic converter, a particulatefilter, or some other element in the exhaust-gas after-treatment system.

According to another concept of the invention, an exhaust-gasafter-treatment system with a connected internal combustion engine isproposed, wherein the internal combustion engine has a motor controlsystem and the exhaust-gas after-treatment system has at least oneregulated catalytic converter and an oxygen accumulator, wherein a firstprobe is arranged before the oxygen accumulator and a second probe isarranged after the oxygen accumulator, wherein the first probe detects afirst parameter characterizing an oxygen content, a signal transmissionof the parameter recorded by the first and second probes to anevaluation unit is provided, and the evaluation unit is coupled with amotor control system with a regulation or control unit that takes intoaccount a rich-lean cycle based on the determined parameter.

By means of such an exhaust-gas after-treatment system with connectedinternal combustion engine, the method described above is preferablyperformed for operating a motor-vehicle exhaust-gas after-treatmentsystem.

One improvement provides that the second probe is a temperature probewhose parameter is included in a control or regulation system of alambda value of the motor control system. Advantageously, a rich-leancycle is included as a desired value in a lambda regulation of theinternal combustion engine.

Another configuration of the exhaust-gas after-treatment system providesthat the first and the second probes each determine a first parametercharacterizing an oxygen content, and a signal transmission of the firstparameter from the first and the second probes to an evaluation unit isprovided; the evaluation unit determines, from the first parameters, asecond parameter characterizing an oxygen content of the oxygenaccumulator, and the motor control system is coupled with a device forsetting an air ratio in the exhaust-gas after-treatment system, whereinan adaptation of the air ratio as a function of the second parameter isprovided by means of the device.

One improvement of the exhaust-gas after-treatment system provides thatthe oxygen accumulator has a first part and a second part that arearranged in at least two different exhaust-gas after-treatmentcomponents. For example, the oxygen accumulator can be formed from anNOx catalytic converter and also from a particulate filter. These canalso be provided separate from each other. In addition, there is thepossibility that a three-way catalytic converter also includes an oxygenaccumulator or a part of this oxygen accumulator. It is preferred when ameasurement probe is provided for determining a temperature of theoxygen accumulator. This permits a direct coupling of the measuredtemperature for a calculation of the oxygen content of the oxygenaccumulator. For example, this determined temperature value can be usedfor testing the oxygen content set, for example, by means of the oxygenbalance. Alternatively or additionally, the determination of thetemperature of the oxygen accumulator also allows one or more of thethresholds named above to change to influence the rich-lean cycleaccording to the temperature-dependent oxygen storage capacity.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantageous configurations and improvements are specified in thefollowing drawings. The resulting features, however, are not limited tothe individual configurations. Instead, to form improvements, individualfeatures can be combined with those of other configurations of thedrawings and also with features of the above description. Shown are:

FIG. 1, a first schematic view of a first exhaust-gas after-treatmentsystem,

FIG. 2, a schematic view of a second exhaust-gas after-treatment systemwith temperature regulation,

FIG. 3, a schematic diagram of a temperature change through a change inthe operation of an internal combustion engine under consideration ofthe oxygen quantity stored per unit time in an oxygen accumulator of theexhaust-gas after-treatment system connected to the internal combustionengine,

FIG. 4, a schematic view of a control loop for setting a temperaturechange through a change in the use of an oxygen accumulator,

FIG. 5, a schematic view of a third exhaust-gas after-treatment systemthat allows, for example, the prevention of a rich breakthrough by meansof calculating a stored oxygen quantity,

FIG. 6, a schematic diagram of a conventional regulation of aconventional catalytic converter with an oxygen accumulator by means ofa lambda probe arranged at an outlet of the catalytic converter, and

FIG. 7, a changed operation of the catalytic converter from FIG. 6 thatacts as an oxygen accumulator under consideration of a calculated oxygencontent based on a two-point regulation according to the proposedoperating method.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows, in a schematic view, a first exhaust-gas after-treatmentsystem 1 in an example configuration. The exhaust-gas after-treatmentsystem 1 is arranged after an internal combustion engine 2. This systemhas an exhaust-gas train 3 in which, for example, an additional air feed4 and also an additional fuel feed 5 are provided. Both feeds 4, 5 arearranged before a first probe 6, in particular, a lambda probe. Thefirst probe 6 is connected in front of an exhaust-gas after-treatmentcomponent 7 viewed in the flow direction. The exhaust-gasafter-treatment component 7 has an oxygen accumulator 8. In addition,the exhaust-gas after-treatment component 7 can have a catalyticconverter, in particular, a regulated catalytic converter, anNOx-accumulating catalytic converter, a particulate trap, a sulfur trap,and/or some other component that is in the position to change an exhaustgas originating from the internal combustion engine 2. The oxygenaccumulator 8 has a first part 9 and a second part 10. These arearranged, for example, separately from each other in different areas ofthe exhaust-gas after-treatment component 7. For example, the first partof the oxygen accumulator 8 can be arranged in a particulate filter,while the second part 10 of the oxygen accumulator 8 is arranged in anNOx-accumulating catalytic converter. The particulate filter and theNOx-accumulating catalytic converter together form, for example, theexhaust-gas after-treatment component 7. A second probe 11 is arrangedafter this component, wherein this probe can also be, for example, alambda probe. After the second probe 11, viewed in the flow direction,there can be another exhaust-gas after-treatment component that can alsohave an oxygen accumulator. For example, the second probe 11 can be usedfor more than balancing the oxygen content for the exhaust-gasafter-treatment component 7 by determining the corresponding air ratioor the oxygen content after the exhaust-gas after-treatment component 7.The second probe 11 can use, preferably simultaneously, the same signalas an input parameter for the oxygen content or the air ratio for thesubsequent exhaust-gas after-treatment component in the scope of acalculation or balancing. For this purpose, another probe, not shownhere in more detail, is arranged after the following exhaust-gasafter-treatment component. Furthermore, there is the possibility thatone or more other probes are provided in the exhaust-gas after-treatmentcomponent 7. For example, one or more of these probes can also form areplacement of the second probe 11 if, by means of the determinedbalancing, the oxygen content of the region outside of the balancinglimits can be determined. By means of a motor control system 12, inparticular, the air ratio in the exhaust-gas train can be changed underconsideration of the oxygen accumulator 8. The motor control system 12is connected, for example, to a separate control device 13 of the firstexhaust-gas after-treatment system 1. The control device 13 records, forexample, the measurement values provided by the different probes anduses these values in a separate evaluation unit 14. By means of thisunit, the currently stored oxygen quantity can be determined, forexample, by means of oxygen balancing across the oxygen accumulator 8.This value can be forwarded, for example, to the motor control system12. The control device 13 is in the position, in turn, to be able toadapt, for example, also under consideration of the determined currentoxygen quantity, an exhaust-gas strategy in connection with the motorcontrol system 12. This can be incorporated, for example, in such a waythat an ammonia-containing medium is fed in a targeted way by means ofthe control device 13. In particular, the control device 13 is in theposition, together with the motor control system 12, to be able to set aturnover between rich operation and lean operation in the firstexhaust-gas after-treatment system 1 under consideration of the oxygenaccumulator 8. According to another configuration, however,functionality of the control device 13, shown separately, can also beimplemented in a motor control device of the motor control system 12.

FIG. 2 shows, in a schematic view, a second exhaust-gas after-treatmentsystem 15. A control/regulation unit 16 that is coupled, in turn, to theinternal combustion engine 2 is connected to this system. Thecontrol/regulation unit 16 is preferably a motor control device, but canalso be a control device arranged separately from the motor controldevice. Control signals 17 and sensor signals 18 can be exchangedbetween the control/regulation unit 16 and the internal combustionengine 2. A lambda probe 19 is connected upstream in the direction offlow between the internal combustion engine 2 and a catalytic converter20 that contains an oxygen accumulator 8. By means of the lambda probe19, a signal characterizing an oxygen content before the catalyticconverter 20 is fed to the control/regulation unit 16. By means of atemperature sensor 21 that is arranged after the catalytic converter 20,viewed in the direction of flow, a temperature signal is also fed to thecontrol/regulation unit 16. By means of this device, showing the mostimportant components of an exhaust-gas after-treatment system 15 onlyschematically, it is possible to perform temperature regulation of theoxygen accumulator 8. In particular, this device made from secondexhaust-gas after-treatment system 15 and internal combustion engine 2allows that a rich-lean cycle can be performed that is influenced by achange of an air ratio and/or a time, a rich phase, and/or a lean phaseso that the oxygen quantity originating from the oxygen accumulator 8per unit time can be changed and therefore a temperature of the oxygenaccumulator 8 and thus also the catalytic converter 20 is regulated orcontrolled.

FIG. 3 shows, in a schematic view, an example of the use of the oxygenaccumulator from FIG. 2 for setting a temperature change of the oxygenaccumulator 8 from FIG. 1 or FIG. 2. In an upper first diagram of FIG.3, the air ratio lambda is shown, plotted on the y-axis, versus time,which is plotted on the x-axis. Under this, the profile of a storedoxygen quantity in the oxygen accumulator is specified, wherein thesolid line running parallel to the x-axis, the time axis, specifies amaximum oxygen storage capacity of the oxygen accumulator. Under this, aconverted oxygen quantity from the oxygen accumulator is also recordedversus time on the x-axis. Under this, a temperature profile of theoxygen accumulator or the catalytic converter that contains, forexample, the oxygen accumulator, is specified, in turn, versus time. Inthe diagrams of FIG. 3 are two different rich-lean cycles set incomparison. A first rich-lean cycle A is characterized with the dashedline in the uppermost diagram of FIG. 3. A second rich-lean cycle B isshown with a dash-dot line. A thin line running parallel to the x-axisspecifies the air ratio lambda=1 in the uppermost diagram of FIG. 3. Thetwo rich-lean cycles A, B differ by an amplitude of a change of therespective air ratio delta lambda. Both cycles have in common that theoxygen accumulator is neither completely filled nor completely emptied.This starts from the profile of the stored oxygen quantity in the oxygenaccumulator that at no time exceeds the maximum oxygen storage capacity.In a lean phase, a stored oxygen quantity increases. This takes place intime period I. In a subsequent rich phase, the oxygen present in theoxygen accumulator is converted with combustible exhaust-gas components.This is shown in time phase II. By setting a high amplitude as shown,for example, in the second rich-lean cycle B, more oxygen is convertedin each rich phase II. Therefore, there is a higher heat flux, so that ahigher temperature increase is set by means of the oxygen accumulator.This is reproduced in the lowermost diagram of FIG. 3. While atemperature at an inlet of the oxygen accumulator remains constant, thischanges at the outlet as a function of the set air ratio or the changein the air ratio, as emerges from the uppermost diagram of FIG. 3.Taking advantage of this relationship, the temperature of the oxygenaccumulator and thus, for example, a catalytic converter can becontrolled or regulated.

In a schematic view, FIG. 4 shows a possibility for implementingtemperature regulation with reference to an action diagram for using theoxygen accumulator. The action diagram provides the internal combustionengine 2 that delivers a time-varying air ratio lambda as a currentstate. The value of the current state of the air ratio is included, onone hand, in an oxygen accumulator 8. By this, a temperature T isdetected by means of a corresponding temperature sensor. Here, thetemperature of the oxygen accumulator 8 and/or a temperature of anexhaust-gas flow can be detected at an outlet from the oxygenaccumulator 8, for example, a catalytic converter, a particulate trap,or another exhaust-gas after-treatment component. The temperature valueis used as a control parameter. This allows a temperature value to beset that specifies a desired value of the temperature to be set in theoxygen accumulator or in the exhaust-gas after-treatment component. Thisdesired value is set, for example, by means of the motor control systemor by means of a separate control device. From the comparison of thecontrol parameter with the desired value, the control difference can bedetermined that is fed as an input parameter to a regulator 15. Fromthis, the regulator generates an amplitude of the air ratio,advantageously in the form of an air ratio change. By means of acorresponding generator, for example, by means of a pulse-widthmodulation generator, a desired value of the air ratio can be formedfrom the change of air ratio delta lambda. This means the correspondingrich-lean cycle delivers the desired value of the air ratio that isincluded together with the current value of the air ratio in a lambdaregulator 16 of the internal combustion engine 2.

As an alternative to the schematic temperature regulation from FIG. 4 ina closed control loop with the required temperature measurement, thereis also the possibility of using a pure control system in which a changein the air ratio is stored in a characteristic map or a characteristicline.

In an example schematic view, FIG. 5 shows a third exhaust-gasafter-treatment system 22 with an internal combustion engine 2 and alsoa control/regulation unit 16, between which control signals 17 andsensor signals 18 can be exchanged. A broadband lambda probe 23 isarranged before an oxygen accumulator 8, for example, in the form of acatalytic converter. Viewed in the direction of flow, a control probe 24is located after the oxygen accumulator 8. The control probe 24 can be abroadband lambda probe or a transition probe. By means of the broadbandlambda probe 23, an air ratio or an oxygen content in the exhaust-gasflow is transmitted with reference to a characterizing parameter to thecontrol/regulation unit 16. From the control probe 24, an air ratio oran oxygen-characterizing signal value is also forwarded to thecontrol/regulation unit 16. This signal can also represent a transitionsignal on the basis of the probe that is used. This configurationallows, on one hand, a determination of the stored oxygen quantity inthe oxygen accumulator 8 by means of balancing across the oxygenaccumulator 8. On the other hand, the configuration is suitable forpreventing a rich breakthrough by the oxygen accumulator 8 and thus, forexample, the connected catalytic converter, with the resulting H₂Semissions, in particular, for desulfurization.

In a schematic diagram, FIG. 6 shows a conventional regulation of acatalytic converter that uses a lambda probe arranged at an outlet. Inthe upper diagram of FIG. 6, the air ratio is shown, and in the lowerdiagram of FIG. 6, the stored oxygen quantity in the catalytic converteris reproduced. All values are plotted versus time. If it is determinedby means of the lambda probe that the air ratio after the catalyticconverter is greater than 1, then a switch point is set at which atransition from lean operation to rich operation is performed. Incontrast, if it is determined by means of the lambda probe that there isan air ratio less than 1 after the catalytic converter, then the controlsystem is switched from rich operation to lean operation. From the lowerdiagram, the respective switch points are drawn using dotted linesdownward from the upper diagram. The substoichiometric orhyperstoichiometric air ratios are advantageously set so that therespectively stored oxygen quantities in the oxygen accumulator havebeen completely removed from the oxygen accumulator or else the storagecapacity of the oxygen accumulator was exceeded. Starting from the upperdiagram of FIG. 6, the desired value of the air ratio before thecatalytic converter emerges as a solid line c. In the dotted diagram a,the actual value of the air ratio before the catalytic converter isshown, while the air ratio after the catalytic converter b is alsorecorded with dashed lines. From this emerges the following relationshipwith respect to the rich-lean cycle that is controlled with respect tothe lambda signal after the catalytic converter: in the lean phase Iwith lambda greater than 1 before the catalytic converter, this and thusthe oxygen accumulator are filled. If accumulation of oxygen in thisphase is not controlled, no oxygen is led through the accumulator andthe lambda signal that is recorded after the catalytic converter as theoxygen accumulator remains at the value of 1. Only when the oxygenaccumulator is completely filled can an oxygen breakthrough be detectedwith reference to the lambda signal and a rich transition can betriggered. In this rich phase II, the accumulator empties. If asufficiently high temperature is provided here, nearly all of thereduction agent is converted, so that the lambda signal again remainsat 1. After complete emptying of the oxygen accumulator, however, areduction agent breakthrough is realized that is indicated by means ofthe probe. Only when this has been detected by the lambda probe can alean transition be realized. Through the inertia provided in the controlpath and in the respective actuators, reduction agent is discharged fora certain time. During desulfurization, this can mean that H₂S isdischarged. In contrast, with the device emerging from FIG. 5, there isthe possibility of preventing such discharge and allowing, inparticular, another type of regulation.

FIG. 7 shows the configuration of 2-point regulation of the oxygenaccumulator that is possible relative to the catalytic converteremerging from FIG. 6. Here, the rich-lean cycle is controlled withreference to the stored oxygen quantity, for example, in the catalyticconverter. This allows rich and also lean breakthroughs to be prevented.Here, preferably, for example, a 2-point regulation with hysteresis isused. When a certain oxygen threshold is exceeded, a rich transition istriggered. When the value falls below another threshold, a leantransition is realized. In the case of desulfurization, at any timethere is sufficient oxygen that can be used for the oxidation of H₂S.The upper threshold 25 and lower threshold drawn in the lower diagramfrom FIG. 7 can thus be guaranteed for sufficient spacing relative to amaximum oxygen absorption capacity of the oxygen accumulator or a safeoperation in all operating points of the exhaust-gas after-treatmentsystem for an emptied state of the oxygen accumulator. From the upperdiagram of FIG. 7 it is to be taken that, in turn, the desired valuebefore the catalytic converter, shown as a solid line c, and also thecurrent value of the air ratio before the catalytic converter, shown asa dotted line a, can lead to an air ratio of lambda=1 after thecatalytic converter for consideration of the oxygen quantity in theoxygen accumulator and thus in the exhaust-gas after-treatmentcomponent. In particular, this permits a constant air ratio b of lambda=1 to be reliably set after the catalytic converter or the exhaust-gasafter-treatment component.

1. A method for operating a motor-vehicle exhaust-gas after-treatmentsystem in which oxygen is fed to or removed from an oxygen accumulatorof an exhaust-gas after-treatment component, wherein at least onechanging parameter defined by the oxygen accumulator and its oxygencontent is determined and is used in the operation of the motor-vehicleexhaust-gas after-treatment system.
 2. The method according to claim 1,wherein an oxygen quantity in the oxygen accumulator is defined.
 3. Themethod according to claim 1, wherein the oxygen quantity in the oxygenaccumulator is incorporated as a parameter for setting a rich-leancycle.
 4. The method according to claim 1, wherein a cyclical change ofa stored oxygen quantity is used for the defined influence of atemperature of the exhaust gas or the oxygen accumulator.
 5. The methodaccording to claim 1, wherein an additional oxygen supply in themotor-vehicle exhaust-gas after-treatment system is performed as afunction of the determined oxygen quantity.
 6. The method according toclaim 1, wherein the oxygen quantity is calculated by means of an oxygenbalancing across the oxygen accumulator.
 7. The method according toclaim 6, wherein a first probe determines a continuous measurement of anoxygen content before the oxygen accumulator, while a second probedetermines whether an exhaust gas is a rich mix or lean mix.
 8. Themethod according to claim 1, wherein for a regeneration of a particulatefilter and/or an NOx-accumulating catalytic converter, the determinedoxygen quantity is included as a parameter.
 9. The method according toclaim 1, wherein for desulfurization of an oxide accumulator, thedetermined oxygen quantity is included as a parameter.
 10. The methodaccording to claim 8, wherein for determining a beginning of thedesulfurization and/or the regeneration, the determined oxygen quantityis included as a parameter.
 11. The method according to claim 8, whereinfor determining a time period of the desulfurization and/or theregeneration, the determined oxygen quantity is included as a parameter.12. The method according to claim 1, wherein a cyclical use of theoxygen accumulator is used for increasing the temperature before adiesel particulate filter regeneration.
 13. The method according toclaim 1, wherein at least one threshold is set with respect to thedetermined stored oxygen quantity, and when this threshold is exceeded,a cycle change between lean operation and rich operation is triggered.14-15. (canceled)
 16. The method according to claim 1, wherein aninternal combustion engine is operated in a rich-lean cycle, wherein atemperature of the oxygen accumulator is determined and an operatingparameter influencing the stored oxygen quantity is changed as afunction of the determined temperature.
 17. The method according toclaim 1, wherein a temperature regulation or temperature control system,with respect to the exhaust-gas after-treatment component having theoxygen accumulator changes an oxygen quantity discharged from orabsorbed in the oxygen accumulator per unit time for adjusting thetemperature of the exhaust-gas after-treatment component.
 18. The methodaccording to claim 1, wherein during desulfurization of anoxide-accumulating catalytic converter, a rich-lean cycle is at leastpartially performed and an air ratio is detected before and after theoxide-accumulating catalytic converter, wherein the oxygen quantity isdetermined and the oxygen accumulator is used to avoid substoichiometryand/or hyperstoichiometry of the air ratio after the oxide-accumulatingcatalytic converter.
 19. An exhaust-gas after-treatment system with aconnected internal combustion engine, wherein the internal combustionengine has a motor control system, and the exhaust-gas after-treatmentsystem has at least one regulated catalytic converter and an oxygenaccumulator, wherein a first probe is arranged before the oxygenaccumulator and a second probe is arranged after the oxygen accumulator,wherein at least the first probe determines a first parametercharacterizing the oxygen content, and a signal transmission of theparameter recorded by the first and the second probes to an evaluationunit is provided, and the evaluation unit is coupled with a motorcontrol system with a regulation or control unit that takes into accounta rich-lean cycle based on the determined parameter.
 20. The exhaust-gasafter-treatment system according to claim 19, wherein the second probeis a temperature probe whose parameter is included in a control orregulation system of a lambda value of the motor control system.
 21. Theexhaust-gas after-treatment system according to claim 20, wherein arich-lean cycle is included as a desired value in a lambda regulation ofthe internal combustion engine.
 22. The exhaust-gas after-treatmentsystem according to claim 19, wherein the first and the second probeseach determine a first parameter characterizing an oxygen content, and asignal transmission of the first parameter from the first and the secondprobes to an evaluation unit is provided, and the evaluation unitdetermines, from the first parameters, a second parameter characterizingthe oxygen content of the oxygen accumulator, and the motor controlsystem is coupled with a device for setting an air ratio in theexhaust-gas after-treatment system, wherein an adaptation of the airratio is provided as a function of the second parameter by means of thedevice.
 23. The exhaust-gas after-treatment system according to claim19, wherein the first probe is a broadband lambda probe and the secondprobe is a transition probe.
 24. The exhaust-gas after-treatment systemaccording to claim 19, wherein the oxygen accumulator has a first partand a second part that are arranged in one or at least two differentexhaust-gas after-treatment components.
 25. The exhaust-gasafter-treatment system according to claim 19, wherein the oxygenaccumulator is a component of an NOx catalytic converter or aparticulate filter.
 26. (canceled)
 27. The exhaust-gas after-treatmentsystem according to claim 19, wherein a measurement probe is providedfor determining a temperature of the oxygen accumulator.
 28. Theexhaust-gas after-treatment system according to claim 22, wherein atleast one of a control system or a regulation system is included and isgeared toward the second parameter, in order to trigger a change betweenrich and lean operation. 29-32. (canceled)